Pressure gauge with digital displays have been utilized for years. Traditional electronic pressure gauges typically include a pressure transducer 20, an amplifier 21, an analog-to-digital (referred as A/D hereinafter) converter 22, a microprocessor (CPU) 23, a driver 24 for driving the display, a light emitting diode (LED) or a liquid crystal display (LCD) 25 for displaying the measured tire pressure, a battery-supplied power control circuit 26 for energizing the electronic circuitry and converting the digital signal into a numerical reading, and a buzzer 28 as shown in FIG. 1, wherein the transducer 20 suffers the stress due to an imposed pressure, the amplifier 21 is connected to the transducer 20 to amplify the analog signal generated from the transducer 20 according to the change of the imposed pressure, A/D converter 22 is connected to the amplifier 21 to convert the analog signal into a digital signal, and the digital display 25 is connected to the A/D converter 22 to display a digital reading in accordance with the digital signal.
Moreover, four electrically interconnected piezoresistors 11, 12, 13 & 14 are utilized in the transducer 20 to form a Wheatstone bridge, as shown in FIG. 2. The resistance of the two piezoresistors 11 and 13 on the Wheatstone bridge increases with the increased pressure applied thereto while that of the other two piezoresistors 12 and 14 decreases, and vice versa. An analog voltage is generated according to the potential difference between the junctions 15 and 16 within the Wheatstone bridge as depicted in FIG. 2, and the analog voltage is amplified by the amplifier 21 and thereafter digitized by the A/D converter 22.
The obtained digital signal in response to the imposed pressure is transmitted into a suitable electronic controller such as the microprocessor circuit CPU 23. The CPU 23 controls the driver 24 to convert the digital signal into the numerical reading displayed on the display 25.
An audible signal device 28 will beep to remind the user when the maximum pressure is detected. Besides, the pressure gauge utilizes at least one battery as a power source which is manipulated by an interconnecting power bus 27 and a power control circuit 26 electrically connected thereto. The power control circuit 26 is in turn operated by the CPU 23.
The prior art of pressure gauges with digital displays includes:
1) U.S. Pat. No. 4,250,759 and B1 4,250,759 both entitled "Digital Readout Gauge" issued to Vago et al., and referred as Ref. 1 and Ref. 2 accordingly hereinafter; PA0 2) U.S. Pat. No. 4,704,901 entitled "Tire Pressure Gauge" issued to Rocco et at., and referred as Ref. 3 hereinafter; PA0 3) U.S. Pat. No. 4,784,845 entitled "Tire Pressure Gauge", which is the Continuation application of U.S. Pat. No. 4,704,901 issued to Rocco et al., and referred as Ref. 4 hereinafter; and PA0 4) U.S. Pat. No. 5,394,343 entitled "Electronic Tire Gauge" issued to Tsao, and referred as Ref. 5 hereinafter.
Ref 1 and Ref. 2 disclose a pressure gauge wherein a pressure transducer is stressed by an imposed pressure and provides an analog voltage which is further amplified by an operational amplifier and then passes to a capacitor wherein the analog voltage with a peak value is held which subsequently passes to an A/D converter to be converted into a digital voltage in the form of binary bits. Then the digital voltage in binary form is passed to a segment decoder to be converted into a decimal form to drive the display numerals of the digital readout display.
Ref. 3 and Ref. 4 disclose a pressure gauge wherein a pressure sensor, such as a piezoresistive transducer, is subjected to an imposed pressure and generates an analog output signal which is further fed through an amplifier and an A/D converter, and the resulting digital signal is directed to a microprocessor circuit (CPU) which controls a driver circuit that in turn drives the visual reading on a numerical display.
Ref. 5 discloses a pressure gauge wherein a periodic (cyclic) signal with a constant low frequency is generated from a voltage-controlled triangular wave oscillator (VCO) circuitry for serving as a reference signal, and the ramp down portion of the VCO waveform is employed for being compared with the analog voltage signal generated from the transducer in response to the imposed pressure. A signal representing the compared result is obtained by a comparator which comprises a micro-processor including programs and a clock defines the signal cycle.
Nevertheless, the electronic pressure gauges with the digital display mentioned above, owing to the great improvements on the reliability and readability of readings, are overwhelmingly superior than those of mechanical measurement system. However, potential shortcomings of those electronic pressure gauges still exist, e.g.,
1. significant errors resulting from the analog-to-digital converting process are unavoidable; PA1 2. more electronic elements and components are required to construct a desired circuit; and PA1 3. relatively higher manufactured costs being involved due to more electronic elements and components are needed. PA1 4. owing to the increased complexity, more bugs are probably encountered during the hardware circuit layout and implementation as well as software programming. PA1 (1) an RC oscillating circuit is employed for generating the pressure signal in response to the imposed pressure; PA1 (2) the A/D converter used in Ref. 1 to Ref. 4 is unnecessary; PA1 (3) the VCO circuit employed for generating the reference signal and the comparator used for obtaining the compared result in Ref. 5 are also unnecessary.
This invention proposes a new pressure gauge with a digital display. The major differences of this invention from the prior art include that:
Thereby, not only is the circuitry simplified but also the above-mentioned disadvantages are overcome.